This invention relates to an image sensor, in particular an image sensor comprising a two-dimensional.
EP-A-233104 and U.S. Pat. No. 4,945,242 describe image sensors comprising a two-dimensional array of imaging elements arranged in rows and columns with each imaging element comprising a two terminal component for sensing light incident on the imaging element and for storing charge representing the incident light and a cathode electrode, and a plurality of row and column conductors with one of the two terminals of each component in a row being coupled to the associated row conductor and the other one of the two terminals being coupled to the associated column conductor, and means for applying voltage signals to the row and column conductors for enabling light incident on the array to be sensed and to enable charge stored at a selected imaging element to be sensed.
A problem with such an image sensor is that during read-out of the charge stored at a selected pixel or imaging element, a leakage current also flows in unselected pixels and so there is a high vertical cross-talk between pixels. One solution to this problem is to ensure that the image sensor is receiving no illumination when the charge stored at the imaging elements is being read-out. Where the image sensor operates by illuminating an object to be imaged, for example a document, this can be achieved by switching the illuminating light source on and off. However there are situations where light will inevitably be falling on the array during readout of the stored charge, for example when the array is viewing a scene rather than a document, and then illuminations cannot be avoided without placing a shutter or aperture in front of the image sensor.